Call distributing telephone system



June 2l, 1938. s. F. DUNNING CALL DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheets-Sheet l WWW Wm T A June 2l, 1938. s E DUNNlNG 2,121,498

GALL DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheecs-SheecI 2 Humm 'IHM Us 1 E 2 51PM/NNW@ Bm' www A TTORNE Y /NVEN TOR Jne 21, 1938. s. F. DUNNING 2,121,498

CALL DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheets-Sheet 3 Q /NVEN TOR SML sf DUNN/NG .B VM A T TORNE V June 2l, 1938. s. F. DUNNING l 2,121,498

CALL DISTRIBUTING TELEPHONE SYSTEM nwmuw'im' 1*' lo lo /N VEA/ron 5.5 DUNN/NG A T TORNE V June 2'1, 1938.v

S. F. DUNNING CALL DISTRIBUTING. TELEPHONE SYSTEM Filed Jull,r 27, 1957 14 Sheets-Sheet 5 /NVENTo/e 5f. DUNN/NG BV- f i s ATTORNEY June 21, 1938. s. F. DUNNING 2,121,498

GALL DSTRIBUTING TELEPHONE SYSTEM 'Filed July 27, 1957 14 sheets-sheet e /NVENTOR SJ? DUNN/NG A T TOR/VE Y June 2l, 193,8-

s. F.,DUNN1NG ,7 2,121,493

f CALL DISTRIBUTING' TELEPHONE SYSTEM l Filed July 27, i957 14 sheets-sheet 'l'v /NVENTOR S. E' DUNN/NG June 21,1938. f SEDUNMNG'. 2,121,498

CALL DISTRIBUTING TELEPHNE SYSTEM F:1led July 27, 1957 14 Sheets-Sheet 8 /NvE/vroR 5.,? DUNN/NG,

mi w21 ATTORNEY June 21, 19.38. F, DUNNlNG y 2,121,498

CALL DISTRIBUTING TELEPHONE SYSTEM f Filed July 27, 1957 14 Sheets-Sheet 9 o ,In Q .o p\

T OLAR/ZED l 'Il /N VEN TOR BK'' i; ATTORNEY June 21,1938. SRDUNMNG 2,121,498

CALL DISTRIBT'ING TELEPHONE SYSTEM F Filed July 27, 193?Y 14 Sheets-Sheet 10 A TTORNE V .June 2l, 193,8.` s. F. DUNNING 2,121,493

GALL. DISTRIBUTING TELEPHONE SYSTEM Filed July 27, 1937 14 Sheets-Sheet ll /N VEA/ron DUNN/NG ATTORNEY L Jun@T 2.1, 1938. Q F, DUNNlNG 2,121,498

CALL DISTRIBUTING TELEPHNE SYSTEM Filed Jlglly 27, 1937 14 Sheets-Sheet l2 1o key ser #2 /NVENTOR DUNN/NG S. F. DUNNING CALL ISTRIBUTINGTELEPHONE SYSTEM June 21, 1938.

FiledvJuly 27,1937 14 Sheets- Sheet 13 /NVE/VTOR 5f DUNN/NG BV l ' ATTORNEY s. F. DUNNING GALLIy DISTRIBUTING TELEPHONE SYSTEM Ju'ne 2l, 1938.

14 Sheets-Sheet 14 Filed July 27, 1937 I I I I I I II A 7` TORNE V Patented June 2l, 1938 UNITED STATES CALL DISTRIBUTING TELEPHONE SYSTEM Sanford F. Dunning, Wheaton, Ill., assigner to American Telephone and Telegraph Company, a corporation of New York Application July 27, 1937, Serial No. 156,029

12 Claims.

This application relates to telephone systems and has for its object to increase the efficiency of such systems.

In systems of the type disclosed in Patent 1,517,260 granted to F. A. Stearn, December 2, 1924, calls originating in a manual oilice for completion in a full mechanical oilice are handled at the terminating cnice by an operator known as the B operator. A plurality oi trunks appear at cach B operators position in listening keys and corresponding lamps. A call incoming on one of these trunks lights the associated lamp and the B operator connects her headset with that of the originating operator by depressing the listening key individual to the trunk.

In accordance with the present invention, the efficiency of this.V system is greatly improved by distributing the calls on a straightforward basis to operators positions common to all trunks. This increases the erliciency of the switchboard since it tends to distribute evenly the incoming calls over the occupied positions resulting in economical operation during the most busy periods.

More specically, the incoming trunks, arranged in groups, are served by a corresponding group of link circuits which in turn are served by a common position lnder circuit. As calls reach trunks in the group, an allotted idle link circuit connects with the calling trunk and then appropriates the position nder circuit for its individual use.

Furthermore, in accordance with the present invention, if a second call is received in the group while the rst call is being served, a 'second link circuit will be allotted, will hunt for and connect with the second calling trunk and will then wait until the position finder circuit is freed by the iirst link. When the position .finder circuit is released, the presence of the second call holds the position nder switch in its last used position and prevents the release of the operators position.

This and other features of the present invention will be more clearly understood from a consideration of the following description in connection with the drawings in which:

Fig. 1 shows the manner in which Figs. 3 to 15 should be arranged to disclose the invention;

Fig. 2 is a diagrammatic showing of the circuits serving one trunk group; and

Figs. 3 to l5 show enough detailed circuits for a clear understanding of the invention, Fig. 3 showing an incoming selector, Figs. fi and 5 showing one link circuit, Fig. 6 showing the position ndcr control circuit, Fig. 7 showing certain timing and alarm circuits associated with the link circuit, Fig. 8 showing the position finder and key-set selector, Fig. 9 showing the operators position circuit, Fig. 10 showing `the calls waiting alarm circuit, Figs. 1l and 12 showing the allotter circuit, Fig. 13 showing one operators key-set and Figs. 14 and 15 showing the key control circuit.

Referring first to Fig. 2 a group of one hundred trunks, 200, 20|, etc. terminating in incoming selector circuits 202, 203, etc. and incoming selector switches 204 are served by a pair of allotter circuits 205 and 206 and by link circuits 201 to 2li. With both allotters in service the allotter 206 allots links 209, 210, 2li which are located on the front of the link frame While allotter 205 allots links 201 and 208 on the rear of the frame. Each link has access to the one hundred trunks of the group over the trunk finder bank 212 and to one hundred senders over the sender selectorbank. 2|3. The ve links 201 to 2H are connected in multiple over the transfer switch 2i 4 to a position nder circuit. Normally, they are connected to position nder circuit 2HE which in turn controls two switches 2|6 and 2li, switch 211 having access to the operators positioncircuit 210 and switch 216 having access to the key control circuit 219. An emergency position finder circuit 220 is provided which may be substituted for the regular position iinder by means of transfer switch 2M. Other groups of links are indicated which also have access to the operators position through their position iinders. The operators position may also be seized by a sender test frame 22|. The incoming selectors have access to called subscribers lines such as line 222 through final selector frames, such as frame 223.

Briefly the operation is as follows: A call incoming on a trunk such as trunk 200 causes a preallotted link, for example link 201, to hunt for the trunk and to simultaneously hunt for an idle operators position. When the position is found, the key control finder is advanced to the corresponding position. The B operators position is then connected through to the originating operators position and the wanted number wis transmitted, while at the same time the link hunts for an idle sender. As soon as the wanted number is received the B operator operates her key-set and is then disconnected from the link. When an idle sender is found the key-set is connected thereto and the number recorded in the sender. The key-set is then released, and under the control of the sender, the incoming and nal selectors are operated to complete the connection with the called line after which the sender and link circuit may restore to normal.

Before describing the detailed operation of the circuits shown in Figs. 3 to l5 certain features of the equipment will be discussed. As mentioned above, two allotters are provided for the link group and they are used alternately one normally allotting the three links on the front of the frame in succession after which the other allotter successively allots the two links on the rear of the frame. However, either allotter may be removed from service and the other allotter made to assign all links. To this end each allotter is equipped with three jacks, for example, the allotter of Fig. 12 is provided with jacks |204, |205 and |206, while the allotter of Fig. ll is provided with jacks |||2 and |||3. A double plug |201 connects jack |206 with jack |208 connected with the two rear links, while the double plug |||4 connects jack |||3 with the jack MI5 extending to the three front links. Under normal conditions the plug |203 is inserted in the jack |204 and the plug |IIO is inserted in the jack I but if either allotter is to be removed from service, for example the allotter of Fig. 12, plug |203 will be removed from jack |204 and inserted in the jack |205. Simi larly if the allotter of Fig. Il is to be removed from service plug |||0 will be removed from jack and inserted in jack |||2. Similar multicontact plug and jack connections are used between the key control selector and the key control circuit and also between the key-set and the key control circuit. In general, these plug and jack connections will be omitted in tracing the circuits hereinafter.

The sender indicated at 550 in Fig. 5 differs from that shown in the patent to Stearn above referred to only in that the battery and ground supply to the registration circuits is reversed between digits to minimize contact injury.

Referring now to Figs. 3V to 15, inclusive, the link circuit of Figs. 4 and 5 when idle and not allotted stands with its sequence switch 500 in position l1. The connection shown between this link and the allotter of Fig. 11 identifies it as the rst link on the front of the link frame. When the last link on the rear of the frame has connected with an operators position it connects ground to conductor |2| l, advancing sequence switch |200 of the rear allotter to position 1. Sequence switch H00 of the front allotter has been standing in position 8, therefore the advance of switch |200 to position 1 closes a circuit from ground over the lower right and upper left contacts of cam |2|2, through jack |204 and plug |203, upper right contact of cam ||02 to the winding of sequence switch magnet |00 and battery, advancing the sequence switch to position 9. It is at once advanced to position |0 in a circuit extending from battery through the winding of sequence switch magnet H00, lower right contact of cam IIIE, conductor ||I1 which extends in multiple to all five link circuits and may be traced in the link circuit shown over the inner upper normal contact of key 400, to ground over the lower left contact of cam 509 and the lower right contact of cam 504. When sequence switch 00 reaches position |0 a circuit is closed from battery through the winding of sequence switch magnet |200, upper right contact of cam IZIS, through jack and plug |||0, upper left and lower right contacts of cam 0 to ground at the inner lower back contact of relay H05.

Sequence switch |200 is advanced to its waiting position, position 3, by this circuit.

With sequence switch H00 in position l0 (or position I) it closes a circuit from ground at the upper back contact of relay H05, plug |203 and jack |204, upper contacts of cam |209, jack |204 and plug |203, upper contacts of cam H04 to conductor H20 individual to the link of Figs. 4 and 5, which extends over the middle lower normal contact of key 400, lower right contact of cam 506 and cam 545 of sequence switch 500, auxiliary Contact of jack 406 in parallel with the lower back contact of relay 4|4, winding of magnet 500 to battery. Sequence switch 500 advances to position by this circuit, in which position the link is ready for use on an incoming call.

It may be noted that the contact of jack 406 and the contact of relay 4|4 are included in the circuit of sequence switch magnet 500 for a purpose to be explained later. Since these contacts appear. in each circuit, they will, for brevity, be omitted from the circuits for magnet 500 to be traced hereinafter.

Assuming that the incoming selector circuit of Fig. 3 is seized at the originating oflice, a circuit is closed from battery in that oflice over the ring conductor 30|, upper left winding of repeating coil 303, through the upper and lower windings of relay 30d in series, lower left winding of repeating coil 303, tip conductor 305i and thence to ground at the originating office. Relay 304 operates in this circuit. If no other call is waiting for service, so that relay is unoperated, relay 300 closes a circuit from battery through the winding of relay 306, front contact of relay 304, right contacts of sequence switch cam 3|3 to conductor 301 and thence to ground at the upper back contact of relay 100. Relay 305 in operating opens one connection to the group busy circuit and prepares circuits to be used hereinafter. Relay 304 closes a circuit, in parallel with the winding of relay 306, from battery through the upper winding of relay 308, lower right contact of cam 309, lower left contact of cam 3|0, front contact of relay 304 and thence to ground as previously traced. Relay 308, in operating, closes a circuit from battery through the winding of sequence switch magnet 300, upper right contact of cam 3| lower front contact of relay 308 to ground over the lower contacts of cam 3|2. Sequence switch 300 advances to position 2 by this circuit. When the sequence switch reaches position I3@ a locking circuit for relay 306 under the control of relay 304 is closed, which may be traced from battery through the winding of relay 306, front contact of relay 304, upper contacts of cam 3|3 to ground at the front contact of relay 306.

When sequence switch 300 reaches position 2 ground is connected over the lower contacts of cam 3|4 to start conductor 3| 5 leading to the link allotter circuit where it extends over the contact of key 10|, to conductor 150 and over the auxiliary contact of jack 102 to the winding of relay 100 and battery. Relay 100, which is common to the group of incoming selectors, operates in this circuit opening the operating circuit for relay 306 and removing ground from similar circuits to other selectors. Relay 100, therefore, prevents any subsequent calls on trunks of the trunk group from advancing their incoming selector sequence switches to the start position until such time as all selectors which advanced before its operation have been served.

The operating circuit of relay 308 is opened in position 2 of sequence switch 300 and therefore relay 3&8 now releases. With relay 388.' released, ground is removed from conductor SI5, to mark this selector as calling.

The ground connected to conductor '|50 is also applied over the lower .back contact of relay ilii, to conductor li i9. This conductor is connected in multiple to all of the link circuits but since sequence switch 5t@ is the lonly switch standingin position i, being the one allotted for use, a circuit will be completed over the lower normal contact of key 400, lower contacts of sequence switch carnllil, winding of relay 5M and battery. Relay Elli operates and closes a circuit from battery through the upper winding of relay it, lower contacts of cam M5, outer right iront contact of relay Eti toground over the right contacts of cam 51M. Relay 4M operates and in turn closes a circuit from battery through the winding of sequence switch magnet 500, upper contacts of cam 565 to ground at the upper front contact or relay 604, advancing sequence switch 509 into position 2. With sequence switch 5b@ in position 2, a circuit is closed from battery through the winding of up drive magnet 4N) of the trunk finder i), upper left and lower right contacts'of cam M95, outer right front contact of relay 50i to ground over the right contacts of cam 5P advancing the line finder in search of the incoming trunk of Fig. 3 which has been marked by the removal of ground from conductor dit. Relay 5S! is held operated over its inner right front contact,v lower contacts of cam 502, commutator strip itl and brush 442 to ground between sets of terminals and over the upper contacts of cam 5&3, normal contact of relay ller, brush @t3 and the upper. contacts of cams like earn Sil to ground as it passes trunks which are not in calling condition.

When the calling trunk of Fig; 3 is found and the brushes of trunk finder 459 are centered, relay 5M releases opening the circuit of the up drive magnet tit, and bringing the trunk iinder to rest. The release of relay 5M also connects ground over its right back contactv to brush. 403 to mark the incoming selector as busy. In ad dition it closes a circuit from battery through the winding of relay M38, upper right and lower left contacts of cam lilil toi ground at the left back contact of reiay 50|. "Ihef operation of relay ttt also closes an obvious circuit for relay lll?. y

The advance of sequenceV switch 569 from po- -sition l opens the operating circuit of relay 431i and thai4 relay releases. With relay Milt released a circuit is closed from battery through the winding of sequence switch magnet 59E, upper right contact of cam 5R36 to ground at the upper back contact ci relay 4M, advancing sequence switch tilill to position 3, in which it remains until the trunk is found as indicated by the operation of relay litt. The operation of relay 408 closes a circuit from ground over its` outer lower front contact, upper left contact of camv 561, to the winding of sequence switch magnet 59E! and battery, advancing the sequence switch to position i With relay M2 operated and sequence switch iiilii in position il, a circuit is closed from, battery through the winding of. relay til@ in the position finder circuit, lower back contact of relay tti, contact 5st of transfer switch 5st, upper contacts of cam di i, outer lower contact of relay il2, trunk finder brush H3, conductor 35i, left contacts of cam 3|3, upper front contact of relay Bilt to ground. Relay Stil operates and closespa holding circuit for itself throughv the winding of relay 63| over the lower front contact yof relay BBQ, switch contact 54%, inner lower back contact of relay llli, upper; left contact of cam 5539 and lower right contact ci cam 594 to ground. Relay till does not operate in this circuit being shunted by the operating circuit of relay litt. Relay tilt closes a circuit from ground over the upper back contact of relay 4M, upper right and iower left contacts of cam M5, upper back contact of relay M32, switch contact 5H), conductor lg, back contact of relay till, inner upper front contact of relay GUEB, switch. contact 5! i, upper right and lower left contacts of cam 5m, outer upper contact of relay M2, brush dit, conductor 32d, upper right contact. of cam 32E to the winding of sequence switch magnet 3D0 and battery, advancing switch 390 to position 3. The advance of sequence switch 300 from position 2. releases relay ltd, restoring ground to conduotor 39T and permitting other incoming selectors to advance to the calling position.

The advance of sequence switch 500 to position 2 as previously described seizes the position finder circuit, if free, by connecting ground to conductor ttt* thereby closing a circuit from ground over the back contact of relay 4M, upper right and lower left contacts of cam M5, upper back Contactl of relay 492, transfer switch contact 529, conductor 5tlg, lower back contact of relay Gi, upper back contact of relay 605, upper normal contact of relay tilt, lower back contact of relay tl'l to the winding of relay 508 and bat tery. Relay Eiif operates and closes a circuit from battery through the winding of relay SIU, outer lower back contact of relay El l, outer upper front contact of relay 598, upper back contact of relay M2', to conductor S539 and thence as previously traced to ground. Relay 08 also pren pares the double test relay till for testing for an idle operators position. It closes a circuit from battery through the lower winding of relay 601, inner upper iront contact of relay 60B, upper winding of relay Gill, inner lower back, Contact of relay 652 and ground to prepare the rela-y for operation. A branch of this circuit extends from ground through the upper and middle windings of relay Sil'i, inner lower front contact of relay GIB to brush 8M of position finder ill. E83 and iii@ close a circuit for relay 653 which may be traced from battery through the winding of that relay over the back contact of stepping magnet il'l, lower back contact of all-positions-V busy relay iiit, upper' front Contact of relay titl,

through the winding of stepping magnet' Btl,

lower front contact of relay Git, lower back contact of relay @lill and thence as' traced for the V circuit of relay tit to ground at the back contact of relay ttl. Magnet till in operating opens the previously traced circuit of relay Bit which in releasing opens the circuit oi magnet Bill and this magnet and relay cooperate until an idle operators position is found.

Such a position is indicated by the presence of battery on a terminal to which brush Bilt has access, which is brought about as follows: When an operator occupies her position, she inserts the plugs of her headset, made up of transmitter Bti] and receiver titl, into telephone jacks and 993 thereby closing a circuit from ground through the right winding of repeating coil Slm,

Relays tip contact of jack 903, transmitter 900, tip contact of jack S02, winding of relay 905 to battery. Relay 905 operates and in turn closes an obvious circuit for relay S which operates and extends battery through resistance 909 over its upper front contact and the outer lower back Contact of relay 953'! to conductor 008 to mark the position occupied. Conductor 908 terminates in the arc served by brush 004 of position nder 800, thereby completing the test circuit through the middle winding 60T which now operates.

Relay |301 in operating opens the cir-cuit of both relay @I3 and magnet 807, bringing the position finder 800 to rest. Relay 507 closes a locking circuit for itself from battery in the operators position as tracedthrougn brush 000, inner lower front contact of relay 6|0, middle winding of relay 60'? to ground at the upper front contact of relay 607. The operation of relay E07 also opens the operating circuit of relay 608 which now releases, and when it closes its lower back contact completes a circuit from battery through the winding of relay S00,

f lower back contact of relay 608, lower front contact of relay 601, normal contact of relay 805, upper back contact of relay 605, lower back contact of relay 604 to grounded conductor 009. Relay 606 locks over its upper alternate Contact to conductor 609 over a part of its operating circuit independent of relays 508 and 001. With relay 606 operated, grounded conductor 000 is extended over the lowerv front contact of relay 6|0, lower front contact of relay 60G, winding of f relay 6| I, brush 803 of the position nder, lower backcontact of relay 9H) or inner lower front contact of relay 006 to the winding of relay 901 and battery. Relay 901 operates in this circuit disconnecting battery from conductor 008 to mark the position busy, lights lamp S25 to warn 1 the operator of an incoming call and disconnects ground from conductors 852 and 853 leading to positions busy circuit.

Relay SII also operates in this circuit, locking over its inner lower front contact, the upper back contact of relay 853 to grounded conductor 609. Relay SII closes a circuit from battery through the winding of relay 305, inner upper front contact of relay 6| I, inner upper back contact of relay 604 to conductor 609. Relay S operates, opening the locking circuit of yrelay 606 and that relay releases. Relay 5| I in operating also closes an obvious circuit for relay 602.

With relay 002 operated, ground is connected to brush 30| of the position nder, and through a terminal engaged by that brush to a corresponding terminal accessible to brush SIG belonging to the key-set nder 8|0 to which the Winding of relay 0|5 is connected. Relay 602 also closes a circuit from ground at its outer lower front contact, lower back contact of relay 6H, back contact of relay 65H5, if the key control circuit has completed its operation on the last previous call, back contact of stepping magnet 8|'| of the key-set nder, winding of relay` 6|6 and battery. As in the case of relay M3, relay BIG operates and closes a circuit for the corresponding stepping magnet SI1 which extends from battery through the winding of magnet 8|?, upper contacts of relay BIE, lower back contact of relay SI5 and thence over the operating circuit of relay 6|6. Relay Slt and magnet 8|'| cooperate as in the case of relay GIE and magnet 801 to advance the key-set finder 8|0 until brush BIS engages the terminal marked by position nder 800 at`which time the circuit of relay ii l 5 is closed and that relay operates, opening the circuit of relay GIG and magnet 8H and stopping the advance of the key-set nder 8|0.

The advance of sequence switch 300 from position 2 opens the operating circuit of relay 600 and permits relay 60| to operate in the locking circuit of relay 600. Relay 60| further opens the operating circuit of relay 600. It also closes ground on the outer lower back contact of relay 002 over the inner upper front contact of relay 60| to conductor 603 leading to the calls waiting signal circuit which will be described hereinafter. The operation of relay 502 in response to the engagement of the operators position removes this ground from conductor 303.

With relays 500, Stil and 605 operated a signal is transmitted to the incoming trunk to connect the A and B positions together. A circuit is closed from battery through resistance 6|9, lower back contact of relay SIB, lower front contact of relay 605, outer upper front contact of relay 60|, inner upper front contact of relay |500, contact 5i I, upper right and lower left contacts of cam 52, upper front contact of relay M2, brush M6, conductor 320, winding of relay 322, lower left and upper right contacts of cam 359, upper back contact of relay 302, left contacts of cam 3H. to ground. Relay 322 operates in this circuit, connecting the tip and ring conductors of the trunk circuit over conductors 325 and 324, switch contacts EIS and 5|5 of switch 590 to condensers 620 and 62| and thence over the upper front contacts of relay 502, brushes 805 and 866 of the position finder, to the terminals of choke coil 9| I, the armatures of relay 0|3 and over the back contacts thereof to the secondary winding of tone coil 92|. Relay 322 also closes a circuit from ground over its outer lower front contact, conductor 323, switch contact 5M, inner upper front Contact of relay 602, brush 802, winding of relay SIB and battery.

Relay 9|0 in operating initiates the operations which result in the transmission of two zip tones to the A operator and the connection of the two operators headsets in talking relation. Relay 9| 0 closes a circuit from ground over its outer upper front contact, normal contact of relay 9|4, resistance SI5, winding of relay 9|6 and battery. Relay 9|6 operates and closes a circuit from the tone source through the primary winding of tone coil 92|, lower normal contact of relay 0I'I to ground the lower front contact of relay SI5. At the same time it closes a circuit from ground over its upper front contact, upper back contact of relay 9|3, winding of relay 9H to battery. The closure of the primary circuit of tone coil 92| transmits an impulse of tone current to the originating operators position over the talking conductors as previously traced and thence through the repeating coil 303 out over tip and ring conductors 305 and 30|, respectively. The operation of relay 9H opens the primary circuit of the tone coil thereby terminating the first tone impulse. Relay SI1 extends its operating ground to the winding of relay 9|8 which operates after an interval to reclose the primary circuit of tone coil 92| and to extend the operating ground of relay 9H to the winding of relay 920. Relay 920 after an interval closes a circuit for relay SIS which disconnects the secondary of the tone coil from the talking conductors thereby terminating the second impulse of tone. Relay 9|3 also locks over its inner upper contact to ground at the upper front contact of relay 9|6. With relay 9|3 operated the talking circuit extends over the outer upper front contact of relay 9|3, normal contacts of key 922, ring of jack 903, the operators headset receiver ring of jack 902 and the lower front contact yor" relay 9|3 thereby permitting the A operator to transmit the wanted number to the B operator. The tones transmitted to the A operator are also heard by the B operator through condensers 923 and 924 preparing her now to receive the wanted number.

As soon as the number has been passed the B operator writes it up on her key-set shown in Fig. 13. Assuming that the wanted number is 2793 she will depress key |302 in the thousands row, key |3|1 in the hundreds row, |329 in the tens row and |333 in the units row. When the rst key is operated, a circuit is closed from ground through the winding of relay |400, through the windings oiz the release magnets |35I, |352, |353 and |354 in parallel, right contact of key |302, contacts of sequence switch cam |502, winding of relay |503, resistance |504 and battery. None of these release magnets and relays operate in this circuit, there being insufficient current to operate relay |400 or any of the release magnets and relay |503 being shunted by a circuit extending from battery through resistance |504, over the back contact of relay |503 and in parallel over the normal contacts l34|, |342, |343 and |344 of each of the key strips until a key in each of the strips has been operated. W'hen this occurs, the shunt is removed from relay |503 and that relay operates, closing a circuit from ground over its upper front contact, left contacts of cam |505, upper back contact of relay |403, lower right and upper left contacts of cam |50I, conductor 833, brush 8|3 of switch 3|0, upper front contact of relay 5|5, lower back contact of relay 6|1, to the lower winding of relay 6|8 and battery. Relay 618 operates in this circuit, opening the operating circuit of relay 322 which in turn releases relay 9|0. Relay 9|0 opens the holding circuit of relays 9|6 and 9|3, restoring the tone relays and the operators talking circuit to normal.

In the meantime the operation of relay 005 following the connection with the operators position circuit started the hunt for an idle sender by completing a circuit from grounded conductor 609 over the lower back contact of relay 604, upper front contact of relay 605, lower front contact of relay 00|, switch contact 5|3, lower back contact of relay 103, lower back contact of relay 402, upper contacts of cam 40|, upper winding of relay 404 to battery. Relay 404 operates and closes a circuit from ground over its upper front contact, upper contacts of cam 505, to the winding of sequence switch magnet 500 and battery advancing the sequence switch to position 5. The advance of sequence switch 500 is signaled to the position finder circuit by a circuit extending rom the upper back contact of relay 4| 4, upper contacts of cam 4|5, switch contact 534, winding of relay 604 and battery. Relay 604 operates, opens the locking circuit of relay 605 and prepares a locking circuit for relay 6|8. With sequence switch 500 in position 5 relay 404 closes a circuit from ground over its upper front contact, upper left and lower right contacts ofY cam 505, through the winding of the up drive magnet 5|1 of sender finder 520 for advancing the finder in search of an idle sender. In position 5 the operating circuit of relay 404 is opened, but this relay remains operated in a circuit -through its lower winding, upper left and lower right contacts of cam 4|1 to the centering commutator strip 5|8, brush 541 and ground. It also is held operated in a circuit from battery through its upper winding, upper contacts of cam 4|8, lower front contact of relay 404, upper right and lower left contacts of cam 4|9 and iinder brush 52| as it passes over busy senders. When an idle sender is found and the brushes are properly centered, both holding circuits for relay 404 are opened and that relay releases and closes a 4circuit from ground over its upper back contact, upper right contact of cam 506 to the winding of sequence switch 500 and battery, advancing the sequence switch to position 6.

With relay 0|8 operated to indicate that the number has been completely set up on the keyset and sequence switch 500 in position 6 to indicate that an idle sender has been found, a circuit is closed from battery through the upper winding of relay |403, left contacts of cam |404, conductor 332, brush 0|2, upper front contact of relay 6|8, switch contact 522, right contacts of cam 523, winding of relay 420,,outer upper normal contact of key `400 to ground at the inner lower contact of relay 4|2. Relay |403 operates and locks to its operating circuit through its upper winding and inner upper front contact and the upper contacts of cam |404. With relay |403 operated, sequence switch |500 is advanced from position I in a circuit from battery, through the winding ofA magnet |500, lower left contact of cam |505, outer upper front contact of relay |403 to ground over the left contacts of cam |505 and the upper front contact of relay |503. At the same time, relay 420 y upper right contacts of cam 405 to ground Vat the innermost front contact of relay 420.Y Relay 404 operates and closes a circuit trom Sground over its upper iront contact, upper contacts of cam 505 to the winding of sequence switch magnet 500, advancing the sequence switch to position 1. When sequence switch 500 leaves position 6 it disconnects ground from conductor 509, thereby releasing relays 3|8, 5H and 901 and freeing the operators position unless another call is waiting in the group. Relay 420 also closes a circuit from ground at its second lower front contact over switch contact 524 to the winding of relay 5H and battery. In addition relay 420 prepares the sender recording circuits by connecting brush` 525 of the sender finder over the outer lower front contact `of relay `4,20, switch contact 526, key-set nder brush-314, conductor 334, upper right contact of cam 250| to cam |405; brush 521 of the sender finder over the upper front contact of relay 42,0, switch Contact 528, key-setnder brush 8H, conductor 03|, upper left contact of cam |501 to cam |400. Furthermore, with sequence switch 500 in position 1 brush 529 is connected over the lower right and upper left contacts of cam 42|., lowerV front contact of relay 404, upper left and lower right contacts of cam V450, switch contact 530, key-set finder brush 8|5, conductor 335, to cam |401.

Registration in the sender is controlled by certain circuit conditions set up on these circuits as determined by the operated keys of the key-set of Fig. 13. As the sequence switch |500 lpasses through positions 2, 3, 4, and 5 battery and ground through various resistancesare connected to these circuits. The register relays of `the sender which are not shown are marginal and non-marginal, the marginal relays responding to low resistance conditions, while the nonmarginal relays operate under all conditions. The sender and its operation is disclosed in the above-identified patent to Stearn. Assuming as before that keys |302, |3|1, |329 and |333 are operated with sequence switch |500 in position 2, the thousands digit is transmitted to the sender. The circuit extending to cam |406, which will be called circuit A, extends in two branches, one over the lower right contact of camr |406, through both of windings of relay |408 to ground at the back contact of relay |508. The other branch of this circuit extends over the upper left contact of cam |406, inner right contact of key |302, upper contacts of cam |409 to the lower winding of relay |408, thereby shunting the high resistance upper winding of that relay and creating a low resistance ground condition on circuit A. Relay |408 operates in this circuit and locks to ground at its own upper front contact. The circuit closed to cam |405, which will be identified hereinafter as circuit B, extends over the lower left contact of that cam to the left contact of key |302, resistance |4|9, right contacts of cam |4|1, resistance |4I8 to battery creatinga high resistance battery condition on circuit B. With relay |403 operated the circuit closed through cam |401, which will be identied as circuit C, is extended over the upper right and lower left contacts of cam |401, resistance |4l2, upper front contact of relay |408, resistance 4|0, lower right and upper left contacts of cam |4|| to battery, producing a high resistance battery condition on circuit C.

Relay |408 also closes a circuit from ground over its inner upper front co-ntact through theA Winding of relay |508, right contacts of cam |509 to battery. When relay |408 starts to operate relay |508 is shunted by a circuit over the right contacts of cam |509, upper back contact of relay |508 to ground at the upper' normal contact of relay |408 but this circuit is immediately opened, permitting relay |508 to operate and open the operating circuit of relay |408. When the registration of the thousands digit has been accomplished at the sender, all three registration circuits are opened and relay |408 releases, connecting ground over its normal contact and the upper front contact of relay |508, lower right contact of cam |5|0 to the winding of sequence switch magnet |500 and battery, advancing the sequence switch to position 3 and releasing relay |508.

When the sequence switch |500 reaches position 3 the key-set is ready to transmit the hundreds digit to the sender. In this position circuit A is open at the contacts of key |3|1. Circuit B is extended over the lower right contact of cam |405 through the windings of relay |5|| to ground at the upper back contact of relay |5|2. A branch of this circuit extends over the upper right contact of cam |405, inner right contact of key |3|1, left contacts of cam |42| to the lower winding of relay |5|| in shunt of the upper high resistance winding thereby creating a low resistance ground condition on circuit B. When the sender is ready to receive this digit and completes circuits A, B and C, relay |5|| operates and locks to ground at its own lower front contact. Circuit C extends through resistance |4|2, upper front contact of relay |5||, resistance |5|3 to ground over the lower contacts of cam |5| 4. With sequence switch |500 in position 3 a circuit is closed from battery over the upper contacts of cam IMI, windings of relay |4|4, lower right and upper left contacts of cam |4|5, left contact of key |3|1, upper right contact of cam |4|3 to ground over the lower left contact of cam |5|4. Relay |4|4 operates in this circuit and closes a shunt over its contact and the lower right contact of cam |401 around resistance MM2, thereby transmitting low resistance ground over circuit C.

With sequence switch |500 in position 3 a circuit is prepared from battery over the left contacts of cam |509, through the winding of relay |5|2 to ground but relay |5|2 is prevented irom operating by means of a shunt over its lower back contact and the normal Contact of relay |5| When relay |5|| operates in circuit B, as previously described, it opens this shunt and relay |5|2 operates. As before, the registration of the hundreds digit in the sender causes the temporary opening of all three registering circuits and relay |5|| releases, closing a circuit from ground over its normal contact and the front contact of relay |5|2 to the upper right contact of cam |5|0 and the winding of sequence switch magnet |500, advancing the sequence switch to position 4.

In position 4 circuit A extends over the lower right contact of cam |406, through the two windings of relay |408 to ground at the back contact of relay |508 creating a high resistance ground on circuit A. Circuit B extends over the upper left contact of cam |405, left contact of key |329, upper winding of relay HHG, left contacts of cam |l| to battery. With relays |408 and |4|6 operated circuit C extends over the upper contacts of cam |401, front contact of relay |4|6, upper contact of relay |408, resistance |4|0 to battery over the lower right and upper left contacts of cam |4||, thereby creating a low resistance battery condition on circuit C. As before relay |408 operates relay |508 and, when the sender has completed the registration, is released to advance sequence switch |500 to position 5.

When the sender is ready for the next registration the three registering conductors are extended to the units register in the sender. In. the key control circuit, registering circuit A is extended over the upper right Contact of cam |406, left contact of key |333 to battery over the left contacts of cam |4|1 and low resistance |4I8. Circuit B may be traced over the lower left contact of cam |50I, inner right contact of key |333, right contacts of cam |42I, lower winding of relay |5|| to ground at the back contact of relay |5|2. The normal circuit over the lower right contact of cam |405 to the two windings of relay |5|| is also closed. With relay |5|| operated, a circuit is closed from ground over the lower contacts of cam |5|4, resistance |5| 3, upper front contact of relay |5|| through resistance |4|2 and the lower right contact of cam |401 to connect a high resistance ground to registering circuit C.

Relay |5|| permits the operation of relay |5|2 as previously described and after the completion of the vregistration releases to advance: sequence switch |500 to position When sequence switch |500 reaches position 6, a circuit is closed from battery over the left contacts of sequence switch cam |420, through the windings of the release magnets 35| to |354 to ground over the plug contact |402. At the same time a circuit is closed from ground through the winding of relay |400 to battery over the left 

